This invention relates to display devices, such as field emission displays, plasma displays, and flat panel cathode ray tubes. Specifically, the invention relates to electrode structures for display devices and methods for making the same.
Display devices visually present information generated by computers and other electronic devices. One category of display devices is electron emitter apparatus, such as a cold cathode field emission display (FED). A FED uses electrons originating from one or more emitters on a baseplate to illuminate a luminescent display screen and generate an image. A gate electrode, located near the emitter, and the baseplate are in electrical communication with a voltage source. Electrons are emitted when a sufficient voltage differential is established between the emitter and the gate electrode. The electrons strike a phosphor coating on the display screen, releasing photons to form the visual image.
Focusing the beam of electrons has become important in high resolution field emission displays, where millions of emitters are located in a small area. High resolution displays require small beam size, which can be achieved by focusing the electron beam. Focusing the beam reduces the effect of individual emitters and reduces off-angle beams and mislanded electrons, yielding a more uniform display.
Focusing the electron beam can be easily performed by using a focusing electrode, such as an aperture-type or concentric-type focusing electrode, as described in Kesling et al., Beam Focusing for Field-Emission Flat-Panel Displays, IEEE Transactions on Electron Devices, Vol. 42, No. 2, pp. 340-347 (Feb. 1995), incorporated herein by reference. Aperture-type focusing electrodes comprise a grid network of conducting material with an opening above the emitter that allows the electrons to pass through while simultaneously acting as a lens. See U.S. Pat. Nos. 3,753,022, 5,644,187, 5,235,244, 5,191,217, 5,070,282, 5,543,691, 5,451,830, 5,229,331, and 5,186,670, all incorporated herein by reference. Concentric-type focusing electrodes are formed from conductive grids on the same plane as the gate electrode, but separated by a small gap. See U.S. Pat. No. 5,528,103, incorporated herein by reference. The electrons originating from the emitters are deflected in the desired direction by applying an appropriate voltage potential to the focusing electrode.
A problem with both types of focusing electrodes is the close proximity of the focusing electrode with the gate electrode (also known as the extraction grid). When the focusing electrode is close to the gate electrode, small particles can cause the grid electrode and focusing electrode to short and cause failure. Phosphor particles coming off the anode screen and particles disassociating from getter materials during packaging of a FED are examples of small particles that can contribute to such failure.
The present invention provides an electrode structure for a display device comprising a gate electrode proximate to an emitter and a focusing electrode separated from the gate electrode by an insulating layer containing a ridge. When the focusing electrode is an aperture-type electrode, the ridge is a ledge, i.e., the ridge horizontally protrudes beyond the vertical sidewall of either the gate electrode, the focusing electrode, or both. When the focusing electrode is a concentric-type electrode, the ridge vertically protrudes beyond either the upper surface of the gate electrode, the focusing electrode, or both. The present invention also relates to a display device containing such an electrode structure.
The present invention also provides a method for making an aperture-type electrode structure for a display device by providing a substrate with an emitter disposed thereon, forming a gate electrode proximate the emitter forming an insulating layer over the gate electrode, and forming a focusing electrode over the insulating layer. The sidewall of the insulating layer horizontally protrudes beyond either the vertical sidewall of the gate electrode, the focusing electrode, or both.
The present invention also provides a method for making a concentric-type electrode structure for a display device by providing a substrate, forming a first insulating layer flanking an emitter on the substrate, forming a gate electrode on the first insulating layer and proximate the emitter, forming a focusing electrode on the first insulating layer, and then forming a second insulating layer between the gate and focusing electrodes. The upper surface of the second insulating layer vertically protrudes beyond either the upper surface of the gate electrode, the focusing electrode, or both. The gate electrode and focusing electrode can be made out of the same conductive material layer by forming a dielectric via therein.
The present invention provides the following advantages over the prior art. By providing an electrode structure with an insulating ridge disposed between the gate and focusing electrodes, shorting between the two electrodes is reduced. Thus, the yield enhancement of display devices containing such an electrode structure is increased.